The present invention relates to controllable optical waveguides and optical displays employing such waveguides.
As is well known, an optical waveguide consists (as illustrated in FIG. 1) of a core 1 of a first refractive index n.sub.1 surrounded by cladding 2 of a second lower refractive index n.sub.2. Light propagating in the core 1 will suffer total internal reflection at the interface with the cladding 2 provided that its angle of incidence .theta. is less than the critical value cos.sup.-1 n.sub.2 /n.sub.1. Thus the light is guided within the core. This simple optical analysis assumes (as will usually be the case) that the dimensions of the waveguide are large compared with the wavelength of the light, so that the waveguide behaves in a multimode fashion.